<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title></title>
</head>

<body>
    <div id='d1'></div>
    <button id='btn1'>点击添加btn1事件</button>
    <button id='btn2'>点击移除btn1事件</button>
    <script src='1-基础.js'>
    </script>
</body>

</html>